Historically, telecommunication customers have been selectively interconnected by the well-known public circuit-switched network on a one path per call basis. The circuit-switched network includes end office circuit switching systems, commonly referred to as end office circuit switches, that connect to the individual customers and the toll circuit-switched network that interconnects the various end offices. The toll circuit-switched network comprises a plurality of interconnected transit circuit switching system offices, commonly referred to as toll circuit switches. In response to a call from one customer to another, a single path is established through the circuit-switched network for the exclusive use of the two customers. When the two customers are served by the same end office circuit switching system, that system directly interconnects the customers. When the two customers are in different geographic areas, the end office circuit switching systems that serve the two the customers are interconnected through the toll circuit-switched network. In large population areas, end office circuit switching systems are also often directly interconnected to form local circuit-switched networks, thus avoiding the use of the toll circuit-switched network for local calls. However, the toll circuit-switched network still interconnects the various local circuit-switched networks for long distance calls.
In contrast, packet switching is based on the ability of packet switches to divide the call or, more particularly, a data message into pieces called data packets. Data packets move through a packet switching network from one customer to another via any number of different paths that interconnect the two customers. At the receiving customer, the data packets are assembled in the proper order to form the original message.
Because a data message is broken into similar data packets, the data packets designated for different destinations can move through a packet-switched network on the same facilities with a minimum of interference with each other. Thus, the facilities interconnecting the packet switches of a packet-switched network may be much more efficiently utilized than those of the circuit-switched network. However, most packet-switched networks have been developed to serve small geographic areas with a high density population of data customers. These local packet-switched networks have also typically been built to meet the needs of low volume users; but with the ever increasing numbers of small as well as large volume data users, the need for interconnecting the various local packet-switched networks to establish cross country internetwork communications is enormous. The problem is that the cost of establishing a toll packet-switched network or transmission facilities that connect the local packet-switched networks is equally, if not more, enormous than the need.
In a recent book by Roy D. Rosner, Packet Switching, Tomorrow's Communication Today, Lifetime Learning Publications, Belmont, Calif., 1982, it is suggested that a packet switch, acting as a user terminal, may be integrated with the circuit-switched network to share the transmission facilities of the circuit-switched network. However, the problem still remains of how a packet switch, not to mention a local packet-switched network, interfaces with the circuit-switched network to establish dedicated communication lines through the circuit-switched network. Furthermore, transmission facilities would have to be established between the packet switch and circuit-switched network for each packet switch destination.